Exhaust gas recirculation device of engine

Abstract

An exhaust gas recirculation device of an engine (10) of the invention comprises a first exhaust gas recirculation passage (50) for connecting an exhaust passage (40) and an intake passage (30) to each other and introducing into the intake passage an exhaust gas discharged from a combustion chamber (21) to the exhaust passage, and a second exhaust gas recirculation passage (55) for connecting the exhaust passage upstream of a part of the exhaust passage connected to the first exhaust gas recirculation passage and the intake passage downstream of a part of the intake passage connected to the first exhaust gas recirculation passage to each other and introducing into the intake passage the exhaust gas discharged from the combustion chamber to the exhaust passage. The amount of the exhaust gas introduced into the intake passage via the first exhaust gas recirculation passage is controlled to a first target exhaust gas recirculation amount and the amount of the exhaust gas introduced into the intake passage via the second exhaust gas recirculation passage is controlled to a second target exhaust gas recirculation amount. When a temperature of the flame on the combustion of a fuel is lower than or equal to an allowable upper limit flame temperature, a first reference exhaust gas recirculation amount set depending on the operation condition of the engine, is set as the first target exhaust gas recirculation amount and a second reference exhaust gas recirculation amount set depending on the operation condition of the engine, is set as the second target exhaust gas recirculation amount. When the temperature of the flame on the combustion of the fuel is higher than the allowable upper limit flame temperature, one of the first reference exhaust gas recirculation gas amount and an amount smaller than the first reference exhaust gas recirculation gas amount is set as the first target exhaust gas recirculation amount and an amount larger than the reference second exhaust gas recirculation amount is set as the second target exhaust gas recirculation amount.

Description

TECHNICAL FIELD[0001]The present invention relates to an exhaust gas recirculation device of an engine.BACKGROUND ART[0002]An exhaust gas recirculation device for recirculating an exhaust gas into combustion chambers by introducing into an intake passage of an engine, an exhaust gas discharged from the combustion chambers of the engine to an exhaust passage, is disclosed in the specification of US Patent Publication No. 2009 / 013253. Much inert gas such as carbon dioxide is included in the exhaust gas, and therefore a temperature of combustion of fuel in the combustion chamber is decreased by recirculating the exhaust gas into the combustion chamber. Accordingly, the production of nitrogen oxide along with the combustion of the fuel in the combustion chamber is restricted.[0003]The specification of the above-mentioned US patent Publication discloses the exhaust gas recirculation device comprising an exhaust gas recirculation passage (hereinafter, this passage is referred to as “upstr...

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Benefits of technology

[0010]According to this invention, when the temperature of the flame becomes higher than the allowable upper limit flame temperature, the amount of the exhaust gas introduced into the intake passage via the second exhaust gas recirculation passage becomes large. Accordingly, the concentration of the oxygen in the gas introduced into the combustion chamber relatively decreases. In this regard, compared with the exhaust gas introduced into the intake passage via the first exhaust gas recirculation passage, the exhaust gas introduced into the intake passage via the second exhaust gas recirculation passage early reaches the combustion chamber. Accordingly, compared with the case that the amount of the exhaust gas introduced via the first exhaust gas recirculation passage is increased, an effect of the increase of the amount of the exhaust gas introduced via the second exhaust gas recirculation passage early influences the combustion chamber and the concentration of the oxygen in the gas introduced into the combustion chamber quickly decreases in the case that the amount of the exhaust gas introduced via the second exhaust gas recirculation passage is increased. In this regard, the concentration of the oxygen in the gas introduced into the combustion chamber largely relates to the temperature of the flame. Accordingly, in order to decrease the temperature of the flame, the decrease of the concentration of the oxygen in the gas introduced into the combustion chamber is effective and it is preferred that the concentration of the oxygen can be quickly decreased.

[0015]Further, according to the exhaust gas recirculation device of the engine of the fourth invention of this application, in any of the first to third inventions, when the temperature of the flame on the combustion of the fuel in the combustion chamber is higher than the allowable upper limit flame temperature, the first target exhaust gas recirculation amount is set to zero. According to this invention, compared with the case that the first target exhaust gas recirculation amount is not set to zero, the second target exhaust gas recirculation amount can be set to a large amount. That is, in the case that the concentration of the oxygen in the gas introduced into the combustion chamber should be decreased when the temperature of the flame is higher than the allowable upper limit flame temperature, if the second target exhaust gas recirculation amount can be set to a large amount as possible, the temperature of the flame can be quickly decreased as possible. On the other hand, when the amount of the exhaust gas in the gas introduced into the combustion chamber excessively increases, resulting from the setting of the second target exhaust gas recirculation amount to a large amount, the combustion of the fuel in the combustion chamber may be affected. However, according to this invention, since the first target exhaust gas recirculation amount is set to zero, the degree of the freedom of the setting of the second target exhaust gas recirculation amount to a large amount, becomes large, without affecting the combustion of the fuel in the combustion chamber.

[0017]According to this invention, when the temperature of the flame becomes higher than the allowable upper limit flame temperature, the amount of the exhaust gas introduced into the intake passage via the second exhaust gas recirculation passage is increased. Therefore, according to this invention, because of the same reason as that explained in relation with the first invention, when the temperature of the flame is higher than the allowable upper limit flame temperature, the temperature of the flame is quickly decreased.

[0019]Further, according to the exhaust gas recirculation device of the engine of the seventh invention of this application, in any of the fifth and sixth inventions, when the temperature of the flame on the combustion of the fuel in the combustion chamber is higher than the allowable upper limit flame temperature, the reference exhaust gas recirculation ratio corrected such that the amount of the exhaust gas introduced into the intake passage via the first exhaust gas recirculation passage becomes zero, is set as the target exhaust gas recirculation ratio. According to this invention, compared with the case that the amount of the exhaust gas introduced into the intake passage via the first exhaust gas recirculation passage is not set to zero, the reference exhaust gas recirculation ratio can be corrected such that the amount of the exhaust gas introduced into the intake passage via the second exhaust gas recirculation passage becomes large. That is, in the case that the concentration of the oxygen in the gas introduced into the combustion chamber should be decreased when the temperature of the flame is higher than the allowable upper limit flame temperature, if the amount of the exhaust gas introduced into the intake passage via the second exhaust gas recirculation passage can be increased as possible, the temperature of the flame can be quickly decreased as possible. On the other hand, when the amount of the exhaust gas in the gas introduced into the combustion chamber excessively increases, resulting from the increase of the amount of the exhaust gas introduced into the intake passage via the second exhaust gas recirculation passage, the combustion of the fuel in the combustion chamber may be affected. However, according to this invention, since the amount of the exhaust gas introduced into the intake passage via the first exhaust gas recirculation passage is set to zero, the degree of the freedom of the correction of the reference exhaust gas recirculation ratio such that the amount of the exhaust gas introduced into the intake passage via the second exhaust gas recirculation passage is large, becomes large, without affecting the combustion of the fuel in the combustion chamber.

Problems solved by technology

Accordingly, the production of nitrogen oxide along with the combustion of the fuel in the combustion chamber is restricted.

The specification of the above-mentioned US patent Publication does not clearly disclose a difference in the property between the exhaust gas introduced into the intake passage via the upstream exhaust gas recirculation passage and the exhaust gas introduced into the intake passage via the downstream exhaust gas recirculation passage, however, generally, a pressure and a temperature of the exhaust gas introduced into the intake passage via the upstream exhaust gas recirculation passage are relatively high, while a pressure and a temperature of the exhaust gas introduced into the intake passage via the downstream exhaust gas recirculation passage are relatively low.

As explained above, when the temperature of the combustion of the fuel in the combustion chamber becomes low, the production of the nitrogen oxide along with the combustion of the fuel in the combustion chamber is restricted.

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